Conventionally, hydraulic pressure control apparatuses having direction switch valves for controlling supply and drainage of hydraulic fluid to and from hydraulic actuators, which are spool valves, are known. A typical spool valve is switched between at least two positions in correspondence with movement of a spool. For example, Japanese Laid-Open Patent Publication Nos. 3-172602 and 2004-19873 each describe one such apparatus having a load pressure detection circuit for detecting load pressure in correspondence with operation of a direction switch valve. Also, the hydraulic pressure control apparatus of Japanese Laid-Open Patent Publication No. 2004-19873 has a check valve provided in the load pressure detection circuit for preventing a backflow of fluid.
However, in each of the apparatuses described in Japanese Laid-Open Patent Publications Nos. 3-172602 and 2004-19873, the load pressure detection circuit is formed as a single integrated circuit (see FIG. 1 of Japanese Laid-Open Patent Publication No. 3-172602 and FIG. 1 of Japanese Laid-Open Patent Publication No. 2004-19873). This complicates the configuration of the load pressure detection circuit. Further, a relatively large space is required for arranging the load pressure detection circuit in a housing in which the direction switch valve is incorporated, thus enlarging the housing. Also, in the apparatus of Japanese Laid-Open Patent Publication No. 2004-19873, the check valve must be arranged in the load pressure detection circuit, which is formed as the integrated circuit and thus configured complicatedly. It is thus difficult to install the check valve. This makes it further difficult to suppress complication of the configuration of the load pressure detection circuit and enlargement of the space for arranging the load pressure detection circuit.